The present invention relates to the construction of a vehicle for carrying dense granular material, and particularly to the construction of a double wall for a belly dump trailer.
Cargo boxes of vehicles such as dump trucks and the like are usually constructed with a load-carrying wall consisting of a single thickness of sheet metal, supported, in some cases, by spaced-apart vertical or sloping I-beams or box beams which are usually fastened on the outer side of the single thickness of sheet metal. An example of such prior cargo box construction is provided in Magor U.S. Pat. No. 2,910,322. Such dump trucks and the like, and particularly belly dump trailers used for hauling dirt, straightrun gravel, and similar dense aggregate materials are subject to stretching and eventual rupture of the sheet metal inner wall.
Particularly weak areas of the construction of belly dump trailer cargo boxes are the interior corners where the vertical side walls join the sloping end walls. The repeated shock and stresses of receiving and carrying heavy loads of dirt, gravel, and rocks result in rupture of the loading-carrying walls of such belly dump trailers particularly frequently in these areas of stress concentration.
In order to improve this situation and provide a belly dump trailer cargo box with greater longevity and strength, a greater thickness of interior wall material has been used, or an additional layer of sheet metal has been added to the outside of the walls of the cargo box. These have provided some additional strength and longevity, but have not been completely satisfactory solutions, partly because of the difficulty in fastening together the components of such a double wall, which presents problems of warpage during welding, and inaccessibility of surfaces which need to be welded to one another.
Other types of double sheet metal wall construction have been disclosed in Johnston U.S. Pat. No. 3,185,112, showing an arrangement for construction of a railroad freight car wall including a generally flat outer sheet metal wall and a ribbed inner sheet metal wall. In the Johnston wall construction the ribs on the inner side of the wall are not interconnected with one another except immediately adjacent the flat outer wall. While this type of construction provides some reinforcement of the wall, it is not particularly adapted for use as a wall of a cargo body such as a belly dump trailer. Since the ribs are not interconnected with one another along their length except immediately adjacent the metal outer wall layer the Johnston wall construction is not as rigid as possible. Additionally, assembly of the Johnston wall, because of the shape of the ribs, is complex.
Radey U.S. Pat. No. 3,123,018 provides a wall construction for freight vehicles which is in some respects similar to that of Johnston, including an outer wall consisting of a single layer of material and an inner face having parallel ribs with space between the edges of the ribs for receiving and gripping nails. The vertical ribs are supported by horizontally disposed angle members which are connected at only a few points to the outer sheet metal wall so that loads carried by the ribs are concentrated at only a few points along the outer wall.
What is needed, therefore, is a type of wall construction and a method for constructing a wall for containing dense material in bulk form, which is stronger and stiffer than previously known walls, without requiring the use of thicker sheet metal material or complex assembly techniques. It is particularly desirable to provide a belly dump trailer wall construction which resists tearing at the corner seams between the vertical side walls and the sloping end walls of the cargo box, and it is desirable for such a wall construction to be easily welded together and to present a long-lastingly pleasant outer appearance.